Optical disk drive, and a method of assembling it

ABSTRACT

An optical disk drive comprises an optical pick-up unit ( 5 ) comprising a fixed part ( 7 ) with at least a light source, and a movable part ( 8 ) mounted on a guide ( 9 ) and comprising at least a mirror ( 13 ), a focusing lens ( 14 ), and lens-moving elements. The movable part is adapted to move a focused beam along the disk (D). A PCB ( 17 ) comprises a signal connection to the lens-moving elements on the movable part of the pick-up unit through flexible wires ( 20 ). Only one PCB ( 17 ) is provided which serves as a mounting base for the fixed part ( 7 ) of the optical pick-up unit ( 5 ), the guide ( 9 ), and the drive motor ( 2 ).

The invention relates to an optical disk drive according to the preambleof claim 1.

In the prior art, an optical disk drive generally comprises an opticalpick-up unit, a linear guide, a sub-frame, a spring-mounted frame and adisk drive motor. Signals to and from the optical pick-up unit aretransmitted to and from a printed circuit board (PCB) through aso-called FLEX connection. This connection conducts read, write, servo,and power signals. The amplitudes and sensitivities of these signals arevery different. This leads to crosstalk problems of these signals.

Furthermore, the optical pick-up unit is normally produced in a separateproduction site. If an optical pick-up unit is built into the opticaldisk drive in an another production line, assembly tolerances are addedto the production tolerances of an optical pick-up unit. This results ina non-negligible percentage of rejects in the production, once afterproduction of the pick unit and once after assembly of the drive. Inprinciple, production tolerances and assembly tolerances can compensatefor each other, but due to the testing after production of the pick-upunit this compensation cannot be used since pick-up units will berejected before compensation can take place.

An embodiment of an optical disk drive according to the preamble of theclaim 1 is known, for example, from U.S. Pat. No. 5,214,630. The opticalpick-up unit is split into a fixed part comprising the light source anda movable part comprising at least a mirror, focusing lens, andlens-moving elements. The size and weight of the movable part is reducedsubstantially thereby, so that response times can be reduced as well.Also the flexible signal connection can be simplified.

An object of the present invention is to further improve the opticaldisk drive of the type referred to in the preamble.

The optical disk drive according to the invention is characterized bythe features of the characterizing portion of claim 1.

Due to the presence of only one PCB onto which the components aremounted, there is no need for many connectors, which increases thereliability. The connection to the lens-moving means of the pick-up unitremains, but this is not a sensitive connection. Due to the integrationof the optical pick-up unit in the production and assembly process, onlyone final test is necessary which will reduce the percentage of rejectsand will simplify test procedures.

Preferably, the PCB comprises electronic components that are mounted tothe PCB on a side thereof facing an adjacent housing wall.

The arrangement of the electronic components on a side opposite from theother components, or in other words on the side facing the adjacenthousing wall, keeps the heat of the electronic components away from theoptical pick-up unit, thereby improving reliability and accuracy.Furthermore, it is easier to remove this heat from the drive unit byconduction, which may obviate the need for a cooling fan. If suchcooling fan is not used, no air filter is necessary either. This reducesthe cost and creates possibilities for further miniaturization. Afurther improvement of the removal of heat from the housing is obtainedif the PCB is mounted to the housing through heat-conducting mountingmeans, such as a heat-conducting mat.

An embodiment of the disk drive in which the housing is made of metalnot only improves the heat-conducting properties even more, but alsoimproves the EMC shielding. Due to the better heat removal there is noneed for large cooling openings in the housing wall, which furtherimproves the shielding effect, both for radiation into and out of thehousing.

According to a preferred embodiment, the flexible wires are containedwithin a wire flex which is bendable about one bending axis only, saidbending axis being substantially parallel to the shaft of the drivemotor.

This arrangement of the wire flex means that it can be kept away fromcomponents which are sensitive to EMC or electrical radiation. It isalso renders possible a flatter design of the disk drive.

It is preferred to mount a linear guide for the movable part of theoptical pick-up unit directly on the PCB. This greatly simplifies thedesign. It is made possible due to critical parts being more rigidlymounted on the PCB. The heat-conducting mat, if any, will reducevibrations if shocks occur. A plastic mat will also serve as amechanical filter for high frequencies. The use of a fixed part and amovable part for the pick-up unit will reduce the mass of the componentsaround the moving lens, thus increasing the possible servo bandwidth.

The invention also relates to a method of assembling an optical diskdrive, comprising the steps of providing a housing, a drive motor, and adrive shaft to be mounted within the housing and adapted to engage thedisk for rotating it, an optical pick-up unit comprising a light source,at least a mirror and a focusing lens to create a focused beam, a guidefor moving the focused beam along the disk, and a printed circuit boardconnected to the guide through flexible wires.

According to the invention, first the main electrical components aremounted on one side of the PCB, and then the slide, the pick-up unit,and the drive motor are mounted on the opposite side of the PCB.

This will simplify the assembly of the disk drive unit since it is notnecessary anymore to turn the PCB over. It further reduces assemblytolerances since all mechanical and optical parts are mounted from oneside.

The invention will be explained in more detail with reference to thedrawings showing an exemplary embodiment of the optical disk driveaccording to the invention in a very schematic way.

FIG. 1 is a very schematic sectional side view of an optical disk driveaccording to the invention.

FIG. 2 is a very schematic plan view of the drive of FIG. 1.

The drawing very schematically shows an optical disk drive for readingand or writing an optical disk D. The optical disk may be of any type,for example CD, CD-ROM, DVD or the like, which are readable or writable.The optical disk drive is thus for recording and/or reproducinginformation on the information track of the optical disk D.

The optical disk drive comprises a housing, very schematically indicatedwith reference numeral 1, for accommodating components of the diskdrive. Preferably, the housing 1 is made of metal. The housing 1 has aclosable opening (not shown) for introducing and removing the disk Dinto and from the disk drive.

Within the housing 1 there is mounted a drive motor 2 having a driveshaft 3 and a hub 4 for receiving the disk D thereon in order to allowthe disk D to be rotated by the drive motor 2.

The housing 1 further contains an optical pick-up unit (OPU) 5 adaptedto read information from or write information on the optical disk D bymeans of a focused light beam 6. According to the invention, the opticalpick-up unit 5 comprises a fixed part 7 and a movable part 8. The fixedpart 7 is mounted in stationary position, whereas the movable part 8 ismovable so as to move the focused light beam 6 along the surface portionof the disk D containing information. In the case as shown, the movablepart 8 is movable in radial direction with respect to the disk D bymeans of a linear guide 9 comprising guide rails 10 and supports 11.

The fixed part 7 of the optical pick unit 5 comprises means forproducing the light beam 6, such as a (laser) light source andperipherals. It also comprises means for receiving the beam of lightreflected from the disk D. The output signal of the receiving means isused for reproducing the information on the disk D and also forcontrolling the focused beam 6.

The movable part 8 of the optical pick-up unit 5 comprises a mirror 13for reflecting the light beam 6 and the reflected light beam through 45°and further comprises a focusing lens 14 and actuator means (not shown)in order to move the lens 14 to properly direct and focus the beam 6 onthe optical disk D.

In order to move the movable part 8 along the linear guide 9, i.e. toact as a slide along the guide rails 10, a micro stepping motor 15 isprovided operatively connected to the movable part 8 through a threadedspindle 16. Alternative driving and transmission means are obviouslyequally conceivable.

As is clearly shown in FIG. 1, the drive motor 2, the fixed part 7 ofthe optical pick-up unit 5, and the supports 11 of the linear guide 9 ofthe movable part 8 of the optical pick-up unit 5 are mounted on a singleprinted circuit board (PCB) 17. Thus, the printed circuit board 17 notonly accommodates electronic components and connections to provide forthe electronic control, but also forms a mounting base for the mainparts of the disk drive unit. The stepping motor 15 is also mounted onPCB 17.

The main electronic components 18 of the PCB 17 are mounted on the sideof the PCB 17 facing the adjacent wall of the housing 1, i.e. oppositeto the optical means and the drive means for the disk D. The heat ofthese electronic components can be dissipated by a heat conducting(plastic) mat 19 onto which the PCB is mounted. The heat can beeffectively removed from the interior of the disk drive through this mat19 and the metal wall of the housing 1.

The PCB 17 and the lens actuators on the movable part 8 of the opticalpick-up unit 5 are electrically and electronically connected throughflexible wires combined in a wire flex 20. This wire flex 20 is flexiblein one direction only and, according to the invention, the wire flex 20is bendable about an axis substantially parallel to the drive shaft 3 ofthe drive motor 2 as shown in FIG. 2. The wire flex 20 may be verysimple and may contain as many as four wires which conduct signals ofsimilar magnitudes, thereby reducing or preventing crosstalk problems.

Assembly of the PCB 17 and components is as follows. First of all,electronic components 18 are mounted to the lower side of the PCB 17.Then the drive motor, the supports 11 with guide rails 10 and movablepart 8 and the fixed part 7 are mounted on the upper side of the PCB 17.Finally there is one soldering step in which all connections between thecomponents and the PCB 17 are made. Due to this way of assembling, it isnot necessary to turn the PCB 17 over during production, while theaddition of tolerances are prevented. It requires only one finalmeasurement for testing.

From the foregoing it will be clear that the invention provides anoptical disk drive which is simple, reliable and robust, and which has ahigh performance and a longer lifetime. The method of assembling theoptical disk drive leads to a lower percentage of rejects.

The invention is not restricted to the above-described embodiment asshown in the drawing, which can be varied in several ways withoutdeparting from the scope of the invention.

1. An optical disk drive, comprising: a housing (1); a drive motor (2)and a drive shaft (3) mounted within the housing and adapted to engagethe disk (D) for rotating it, an optical pick-up unit (5), including afixed part (7) comprising at least a light source, and a movable part(8) with sliding mounted possibility on a guide (9) and comprising atleast a mirror (13), a focusing lens (14), and lens-moving elements,said movable part being adapted to move a focused beam along the disk(D), a PCB (17) having a signal connection to the lens-moving elementson the movable part (8) of the pick-up unit through flexible wires (20),characterized in that only one PCB (17) is provided which serves as amounting base for the fixed part (7) of the optical pick-up unit (5),the guide (9), and the drive motor (2).
 2. The optical disk drive asclaimed in claim 1, wherein the PCB (17) accommodates electroniccomponents (18) which are mounted to the PCB (17) on a side thereoffacing an adjacent housing wall.
 3. The optical disk drive as claimed inclaim 1, wherein the PCB (17) is mounted to the housing throughheat-conducting mounting means, such as a heat-conducting mat (19). 4.The optical disk drive as claimed in claim 1, wherein the flexible wiresare contained within a wire flex (20) which is bendable about onebending axis only, said bending axis being substantially parallel to theshaft (3) of the drive motor (2).
 5. The optical disk drive as claimedin claim 1, wherein the linear guide (9) for the movable part (8) of theoptical pick-up unit (5) is mounted directly on the PCB (17).
 6. Theoptical disk drive as claimed in claim 1, wherein the housing (1) ismade of metal.
 7. The optical disk drive as claimed in claim 1, whereinthe movable part (8) of the pick-up unit (5) comprises an actuatorhaving driving coils for the focusing lens, said driving coils beingconnected to the PCB through said flexible wires (2).
 8. A method ofassembling an optical disk drive, comprising the steps of: providing ahousing (1), a drive motor (2), and a drive shaft (3) to be mountedwithin the housing and adapted to engage the disk (D) for rotating it,an optical pick-up unit (5), comprising a light source, at least amirror (13) and a focusing lens (14) to create a focused beam, a guide(9) for moving the focused beam along the disk, and a PCB (17) havingmain electrical components (18) and being connected to the guide (9)through flexible wires (20), characterized in that first the mainelectrical components (18) are mounted on one side of the PCB (17), andthen the guide (9), the pick-up unit (5), and the drive motor (2) aremounted on the opposite side of the PCB (17).
 9. The method as claimedin claim 8, wherein the parts (2, 5, 9) and electrical components (18)are fixed to the PCB (17) in one soldering step.